Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination

This protocol represents the synthesis of silver palladium alloyed nanoparticles supported on zirconium dioxide. It facilitates the harvesting of energy from visible light irradiation to accelerate and control more light colored transformations. This method allows the matching of plasmonic and catalytic properties of a single line of particle to enable light trivalent transformations in catalytic metals that do not have plasmonic properties.

This protocol can give insights into nanocatalysis, nanoparticle synthesis and supported catalyst synthesis. It can be applied to order molecular transformations in nanoparticle compositions. To fabricate silver palladium zirconium dioxide nanoparticles.

Add 50 milliliters of silver nitrate and 9.71 milliliters of potassium tetrachloroplatinate to a 250 milliliter beaker containing one gram of zirconium dioxide. Mix the solutions under vigorous magnetic stirring at 500 revolutions per minute at room temperature for five minutes before adding 10 milliliters of lysine to the beaker. After 20 minutes, add 10 milliliters of a freshly prepared sodium borohydrid solution to the mixture drop wise at a rate of one milliliter per minute.

Continue to stir the mixture for an additional 30 minutes at room temperature then allow the reaction to settle overnight. The next morning, split the suspension between several centrifuge tubes and separate the solids from the mixture by centrifugation. Carefully remove the supernatant and add 15 milliliters of deionized water to the tubes.

Shake vigorously until the solid has been thoroughly dispersed placing the tubes in a vortex for one minute to fully resuspend the material as necessary. Repeat the centrifugation wash and resuspension two more times as demonstrated using 15 milliliters of deionized water for the second wash and ethanol for the third. After removing the ethanol from the last wash, dry the solid in a 60 degrees Celsius oven for 24 hours before characterizing the silver zirconium dioxide preparation by standard microscopy elemental and spectroscopic techniques.

To produce silver zirconium dioxide nanoparticles add 50 milliliters of silver nitrate to a 250 milliliter beaker containing one gram of zirconium dioxide powder under vigorous magnetic stirring at room temperature, add 10 milliliters of lysine to the beaker and continue to stir the mixture for an additional 20 minutes. At the end of the incubation add 10 milliliters of freshly prepared sodium borohydride to the solution as demonstrated for a 30 minutes during incubation at room temperature. For separation and purification of the catalyst split the solution between several centrifuge tubes and collect the solids by centrifugation.

Carefully remove the liquid phase and add 15 milliliters of deionized water to the tubes to allow a vigorous resuspension of the solids. Centrifuge the resulting solution for one additional wash with distilled water and one with ethanol as demonstrated. After removing the ethanol drive a solid in a 60 degrees Celsius oven for 24 hours before characterizing the silvers zirconium dioxide nanoparticles by a variety of standard microscopy elemental and spectroscopic techniques.

To investigate the performance of the plasmonic catalyst under light illumination add 30 milligrams of catalyst to a 25 milliliter round bottom flask with a magnetic stir bar and add five milliliters of a 0.03 mole per liter nitrobenzene in isopropyl alcohol solution. Add 11.22 milligrams of potassium hydroxide powder to the flask and bubble this suspension with an argon flow for one minute to purge the reactor. Immediately after purging, place the sealed flask in a 70 degrees Celsius oil bath above a temperature controlled magnetic stirrer at 500 revolutions per minute.

Use four LED lamps with a 427 nanometer wavelength and a 0.5 watts per square centimeter light intensity placed exactly seven centimeters away from the flask to irradiate the solution. And let the reaction proceed for 2.5 hours at 70 degrees Celsius under vigorous magnetic stirring. At the end of the incubation, turn off the lights and use a syringe and a needle to collect a one milliliter sample from the open reactor.

Then strain the sample through a 0.45 micron filter into a glass chromatography vile to remove the catalyst particulate. To investigate the performance of the plasmonic catalyst in the absence of lighter radiation perform the analysis as just demonstrated but with the reaction container wrapped with aluminum foil to protect it from light. For gas chromatographic analysis prepare 10 milliliters of isopropyl alcohol solution containing approximately 30 millimoles per liter of nitrobenzene, 30 millimoles per liter of aniline and 30 millimoles per liter of azobenzene and run gas chromatography analysis on the solution according to standard protocols.

The selected method should be able to separate the peaks corresponding to isopropyl alcohol, nitrobenzene, aniline and azobenzene in the minimum period of retention time as illustrated. Once the method has been selected prepare individual sets of solutions of 50, 25, 10, five and 2.5 millimolar nitrobenzene, aniline or azobenzene in isopropyl alcohol. Then run a gas chromatography analysis of each of the prepared solutions.

Each chromatogram should present two peaks with the higher peak corresponding to isopropyl alcohol and the lower peak corresponding to nitrobenzene, aniline or azobenzene as appropriate. For each chromatogram note the retention time and peak area of each peak. Then plot the concentration versus peak area of each sample to trace the calibration curve to determine the concentration of each solvent.

Zirconium dioxide does not display bans in the visible range and therefore should not contribute to any photocatalytic activity. A signal centered at 428 nanometers can be detected for the silvers zirconium dioxide nanoparticles while the silver palladium zirconium dioxide nanoparticles display a peak centered at 413 nanometers. It is difficult to identify silver palladium nanoparticles by scanning electron microscopy, but the formation of nanoparticles with a mean particle size of around 10 nanometers can be visualized by transmission electron microscopy.

After the reaction the conversion and selectively for the formation of azobenzene and aniline can be measured by gas chromatography. In the absence of catalysts no nitrobenzene conversion is detected in the presence or absence of light illumination. For silver zirconium dioxide nanoparticles no conversion is detected in the dark while a 36%conversion is observed under LSPR excitation.

A 56%selectivity toward azobenzene is also detected indicating that the silver alone can catalyze this reaction under LSPR excitation. For the bio metallic silver palladium zirconium dioxide nanoparticles no significant conversion is detected under dark conditions. Interestingly, under LSPR excitation the conversion is 63%with a 73%selectivity towards azobenzene, demonstrating the potential of the by metallic configuration to not only increase conversion under LSPR excitation but to also control reaction selectively.

The reaction is catalytically driven by palladium and plus moronically enhanced by silver, under visible light irradiation. Therefore, controlling the nanoparticle synthesis and selecting the light wavelengths for catalysis are important. The catalytically active metal palladium and plasmonically active metal silver can be replaced with other types of possible combinations to target different types of organic reactions.